Block 1, Unit 5, SK320 Infectious Disease and Public Health

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A set derived from the module content of the Open Universities SK320 Infectious disease and Public Health module 2012.

A-B Model

Model of exotoxin structure, where A and B represent different subunits observed in these toxins. B is the binding subunit that allows entry of the toxin into the cell; A is the subunit that causes toxic effects.

Acid-fast

A functional category of bacteria defined by cell wall composition and hence reaction to staining techniques. Mycobacteria fit this category.

Adhesins

Protein or polysaccharide molecules on the surface of many viruses and bacteria that bind to specific receptor molecules (glycolipids or glycoproteins) of the host cell membrane and so attach the microbe to the cell.

Antibiotics

Substances produced by microbes, which interfere with the growth of other microbes (e.g. penicillin is derived from mould). Over time this precise meaning has been diluted to include synthetic antibacterial drugs and sometimes even to refer to any antimicrobial drug; as a result, it's use is being discouraged in medical literature.

Antitoxins

Antibodies that bind toxins and are able to neutralise them.

Axial fibrils

Flagella of some spirochaetes, which are anchored to the bacterium at either end and wrapped around the peptidoglycan layer.

Bacteraemia

A blood stream infection caused by bacteria.

Bacteriocidal

The action of chemicals that kill potantially harmful bacteria in the environment or on the surface of the body; such chemicals are known as this. (The suffixes -cide or -cidal denote killing.)

Bacteriostatic

The action of chemicals that prevent bacteria from replicating in the environment or on the surface of the boody; such chemicals are known as this. (The suffixes -stat or -static denote the cessation of growth or motion.)

Biofilm

A colony of bacteria (or less commonly fungal cells) growing as a continuous adherent sheet on the surface of a substrate, typically glass, polymers or metals. These can be found growing on the inner surface of medical tubing and are a common source of hospital acquired infections. These are also common in the body, e.g. in the colon.

Biotechnology

The use of organisms, their parts or processes, for the manufacture or production of useful or commercial substances.

Commensal

The partner in a symbiotic relationship that benefits from food and possibly shelter while the host remains unaffected.

CRISPR

Clustered regularly interspaced short palindromic repeats. Genetic loci in bacteria that contain many short repeated sequences with short intervening sequences of exogenous DNA (derived from foreign bacteriophages or plasmids). The system acts as a type of prokaryotic 'immune system' by conferring resitance against subsequent exposure to these exogenous DNA sequences.

Endospore

Structures formed by some species of bacteria that enable them to withstand advers conditions. Only species of Bacillus and Clostridium can produce these.

Endotoxins

A class of bacterial toxins, consisting of components (lipopolysaccharide) of the Gram-negative bacterial surface.

Exfoliative

Description of a toxin that causes lysis of the epithelium, and sloughing of the skin.

Fimbriae

(Singular, fimbria) Fine hair-like structures, found mostly on Gram-negative bacteria, which are involved in adhesion. Also known as pilli.

Flagella

(Singular, flagellum) Whip-like organelles that protrude from the cell surface and are used for movement or feeding.

Glycocalyx

The fibrous, outermost layer of the surface of some bacteria that can be involved in mediating attachment to the host.

Gram-negative bacteria

Bacteria that do not retain crystal violet dye in the Gram-staining test.

Gram-positive bacteria

Bacteria with a thick peptoglycan layer in their cell wall that is stained blue-purple by the Gram stain dye.

Haemagglutinins

Surface glycoproteins, found in some viruses and bacteria, with the ability to bind that membranes of red blood cells and cause agglutination (clumping).

Intoxication

The condition caused by the effects of toxins in the body.

Lipo-arabinomannan

Glycolipid consisting of a polymer of lipid and the sugars arabinose and mannose, found in cell walls of Mycobacterium spp.

Lipopolysaccharides

A component of the outer membrane of Gram-negative bacteria that is highly immunostimulatory in mammals.

Lysogeny

The integration of the phage genome into that of it's bacterial host.

Minimum inhibitory concentration

Also known as MIC. The lowest concentration of an antimicrobial agent that will inhibit the visible growth of a microorganism after overnight incubation.

Mononuclear phagocyte system

A collection of phagocytic macrophages, found in the blood and tissues, which trap and eliminate particles foreign in the body.

Mycolic acid

The complex of branched lipids on the surface of Mycobacterium spp.

Outer membrane

Membrane lying outside the cell wall of Gram-negative bacteria.

Pathogenicity islands

Particular regions in bacterial genomes that encode virulence factors. Pathogenicity islands are found in pathogenic bacteria but not in non-pathogenic strains of the same or related species. Iimage shows this region in the salmonellae)

Penicillin

Group of beta-lactam antibiotics derived from penicillium fungi.

Peptidoglycan

Major component of bacterial cell walls. It is a polymer of high molecular mass, composed of two complex monosaccharides derived from glucose, which are linked together by amino acids, including three amino acids that are not found naturally in proteins elsewhere: D-glutamic acid, D-alanine and meso-diaminopimetic acid.

Periplasmic space

Space between the outer membrane and the inner (plasma) membrane, either side of the bacterial cell wall.

Pili

(Singular, pilus) Thin (3-10 nm diameter) extensions of the bacterial wall, made of helically arranged protein monomers, and with a role in adhesions. Also known as fimbriae.

Plasmids

Small autonomously replicating circles of DNA found in many bacteria; some encode functions that enable their own transfer.

Porins

A transmembrane complex of protein and lipid that allows passage of various solutes across the bacterial outer membrane.

Probiotics

Substances, including the living microbes, that promote the health or growth of a human.

Quorum sensing

Bacterial cell-cell communication, correlated to their population density. Bacteria release (species-specific) signalling molecules and infer the density of surrounding bacteria by sensing the accumulation of these molecules. Many bacteria use quorum sensing to coordinate to local population size.

Selective toxicity

The targetting of drugs to affect only the particular type of pathogenic organism, to minimise and damage to host cells, commensal organisms in the host, or harmless organisms in the environment.

Serovars

Groups of closely-related microorganisms distinguished by a characteristic set of antigens. (Also sometimes referred to as serotypes.)

Sheath

Outer membrane of spirochaetes. It is lipid rich.

Siderophores

High-affinity iron-binding molecules, produced by many pathogenic bacteria.

Strains

Types of bacteria or virus within a species that are distinguishable be genotype (nucleic acid sequence) or phenotype, usually determined by the ability of different antibodies to distinguish them (serology).

Systemic infection

An infection that spreads through the body via blood and/or lymphatics.

Transposons

Segments of DNA that are capable of independently replicating themselves and inserting the copy into a new position within the same or another chormosome or plasmid.

Typing

Establishing which strain of a bacterial species is associated with a particular outbreak of disease. May be done by reaction with antibodies (serotyping) or exposure to infection by bacteriophage (phage typing).

Virulence factors

Properties of a microbe that determine it's virulence, e.g. adhesins and exotoxins.

Biotypes

A group of organisms with the same genetic constitution.

Biovars

A group of bacterial strains that are distinguishable physiologically or biochemically from other strains of the same species.

Miasmas

Name from ancient Greek for 'bad air' or 'pollution'. The miasma theory held that disease such as cholera, plague and Chlamydia were air borne, and were caused by bad smells in the air.

Oxidase test

A diagnostic test that is employed to distinguish between different species of bacteria by testing for cytochrome oxidase, using the ability of this enzyme to oxidize the substrate TMPD to produce a purple product.

Ride-water stools

A symptom of cholera. People with the disease often have watery stools, with a vaguely fishy odour, containing flecks of mucus. This substance is said to resemble water from boiled rice, hence the name given to it.

Serovars

Groups of closely-related microorganisms distinguished by a characteristic set of antigens. (Also sometimes referred to as serotypes.)

Slide agglutination test

A diagnostic test used for cholera in which test antiserum against particular O antigens is added (on a microscope slide) to a sample of culture obtained from a patient. If the serum recognises the O antigens in the sample, it binds to them, clumping and immobilising the bacteria.

BCG Vaccination

A live, but weakened, form of Mycobacterium bovis, known as Bacillus Calmette-Guérin. The vaccine is about 80% effective in preventing tuberculosis for a duration of about 15 years.

Consumption

A former name for tuberculosis, which describes how the illness causes dramatic weight loss, 'consuming' the person who has contracted it.

Directly Observed Treatment Short Course

Also known as DOTS. DOTS strategies help ensure people continue taking their TB medication. It is vital that patients being treated for TB complete their course of medication, which can take 6 to 8 months, otherwise the TB can return in a drug-resistant form (MDR-TB).

Granuloma

A small, inflamed area consisting of immune cells and fibroblasts. It forms when the immune system attempts to isolate substances that it perceives as foreign, but is unable to eliminate.

Induration

Localised hardening of soft tissue in the body as a reaction to inflammation.

Isoniazid

An antibiotic used to treat tuberculosis. It is a pro-drug that inhibits the synthesis of mycolic acid, which is otherwise required for the mycobacterial cell wall

Lesions

Areas of damage, injury or change in the function or structure of part of the body.

Mantoux test

A diagnostic tool for tuberculosis. A non-pathogenic extract of Mycobacterium tuberculosis is injected under the skin. A person who has been previously infected with the bacterium should mount an immune response within 48 hours, resulting in localised inflammation at the injection site. The diameter of the reaction is an important parameter in the diagnosis.

MDR-TB

(Multidrug-resistant TB) Tuberculosis bacteria that are resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs.

Military TB

Form of tuberculosis that is characterised by wide dissemination through the human body and by the small size of the lesions (1-5 mm).

Rifampicin

Antibiotic used to treat tuberculosis. It inhibits DNA-dependent RNA polymerase, which is essential for binding to promoter sites in DNA and initiating transcription. Thus, rifampicin inhibits protein synthesis.

Stop TB Strategy

A six-point strategy developed by the WHO to combat tuberculosis: (1) pursue high-quality DOTS expansion and enhancement; (2) address TB-HIV, MDR-TB and the needs of poor and vulnerable populations; (3) contribute to health system strengthening based on primary health care; (4) engage all care providers; (5) empower people with TB, and communities through partnership; (6) enable and promote research.

Streptomycin

Antibiotic drug, first used to treat tuberculosis. Streptomycin is a protein synthesis inhibitor that binds bacterial 16S rRNA and the 30S bacterial ribosome, eventually causing bacterial cell death.

Tubercles

A former name for small hard lumps (granulomas) that are generally within the lungs of people with tuberculosis. They are formed when the immune system attempts to isolate TB bacteria.

XDR-TB

(Extensively drug-resistant TB) Tuberculosis bacteria that are resistant to any fluoroquinone, and at least one of the three injectable second-line drugs (capreomycin, kanamycin, and amikacin), in addition to the two most powerful front-line anti-TB drugs, isoniazid and rifampicin.

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